This section is intended to provide a background to the various embodiments of the technology that are described in this disclosure. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
Radio communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such communication networks support communications for multiple user equipments (UEs) by sharing the available network resources. One example of such a network is the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology standardized by the 3rd Generation Partnership Project (3GPP). UMTS includes a definition for a Radio Access Network (RAN), referred to as UMTS Terrestrial Radio Access Network (UTRAN). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. For example, third-generation UMTS based on W-CDMA has been deployed in many places the world. To ensure that this system remains competitive in the future, 3GPP began a project to define the long-term evolution of UMTS cellular technology. The specifications related to this effort are formally known as Evolved UMTS Terrestrial Radio Access (E-UTRA) and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), but are more commonly referred to by the name Long Term Evolution (LTE). More detailed descriptions of radio communication networks and systems can be found in literature, such as in Technical Specifications published by, e.g., the 3GPP. The core network (CN) of the evolved network architecture is sometimes referred to as Evolved Packet Core (EPC) and when referring to a complete cellular system, including both radio access network and core network, as well as other possible entities, such as service related entities, the term Evolved Packet System (EPS) can be used.
As a mere background only, FIG. 1A illustrates an example 3GPP LTE radio communication system 100. Accordingly, FIG. 1A illustrates a radio access network in an LTE radio communication system 100. In this example, there are two radio network nodes 110a and 110b, each of which is exemplified as an evolved NodeB, eNB. A first eNB 110a is configured to serve one or several UEs, 120a-e, located within the eNB's 100a geographical area of service or the radio cell 130a. The eNB 110a is connectable to a CN. The eNB 110a is also connectable, e.g. via an X2 interface, to a neighboring eNB 110b configured to serve another cell 130b. Accordingly, the second eNB 110b is configured to serve one or several UEs, 120f-j, located within the eNB's 100b geographical area of service or the cell 130b. The eNB 110b is also connectable to a CN.
A currently popular vision of the future development of the communication in radio communication networks comprises huge numbers of small autonomous devices, which typically, more or less infrequently (e.g. once per week to once per minute) transmit and receive only small amounts of data (or are polled for data). These devices are not assumed to be associated with humans, but are rather sensors or actuators of different kinds, which communicate with application servers (which configure the devices and receive data from them) within or outside the cellular network. Hence, this type of communication is often referred to as machine-to-machine (M2M) communication and the devices may be denoted machine devices (MDs). In the 3GPP standardization, the corresponding alternative terms are machine type communication (MTC) and machine type communication devices (MTC devices), with the latter being a subset of the more general term UE. More detailed descriptions of MTC communication can be found in literature, e.g., in the Technical Specification 3GPP TS 22.368 V.12.0.0.
With the nature of MTC devices and their assumed typical uses follow that these devices will often have to be energy efficient, since external power supplies will often not be available and since it is neither practically nor economically feasible to frequently replace or recharge their batteries. In some scenarios, the MTC devices may not even be battery powered, but may instead rely on energy harvesting, e.g. gathering energy from the environment, that is, utilizing (the often limited) energy that may be tapped from sun light, temperature gradients, vibrations, etc. For such energy deprived devices, whose traffic is characterized by relatively small and more or less infrequent transactions (often delay tolerant), it may be important to minimize their energy consumption, e.g. between and in conjunction with the communication events. These devices generally consume energy between the various communication events, e.g. by keeping the radio receiver active to monitor transmissions from the cellular network. Since the periods between the communication events are generally much longer than the actual communication events, this energy consumption may represent a significant part of the overall energy consumption and may even dominate the energy consumption in scenarios where the communication events are infrequent or very infrequent.
The inventors have realized that the actual uplink (UL) transmissions naturally consume significant amounts of energy during the communication events. This may be magnified by the relatively large control signaling overhead that may be associated with a certain communication event, especially since an infrequently communicating MTC device (or other UE) will generally go through the idle to connected mode transition prior to every communication event. FIG. 1B shows a signaling diagram illustrating an example message sequence during the idle to connected mode transition in LTE. As can be seen, the signaling procedure involved during idle to connected mode transition for a UE may be relatively extensive.
A mechanism that has been introduced in radio communication networks in order to save energy in the UEs, e.g. between communication events, is discontinuous reception (DRX), which allows a UE to remain in an energy-saving sleep state most of the time, while waking up to listen for pages in idle mode DRX or downlink resource assignments (i.e. downlink transmissions) in connected mode DRX. Furthermore, in order to make the DRX mechanism even more effective for energy MTC devices, 3GPP is currently working on extending the maximum DRX cycle length, and thus the sleep period, both for idle mode DRX cycle and the connected mode DRX cycle. A DRX cycle thus essentially consists of a sleep period followed by an active period and this cycle is repeated over and over again until the device is detached from the network. Typically, but not necessarily, the sleep period is longer than the active period. A DRX cycle may have a more complex structure than described above, e.g. including a few repetitions of a shorter DRX cycle at the end of the active period, but for the purpose of this disclosure, the simplified DRX cycle description suffices in order to understand the principles of the various embodiments described herein. The idle mode DRX cycle, i.e., the paging cycle, is generally configured in the UE through parameters in the system information (SI) that is broadcast in each radio cell, in conjunction with UE specific parameters in the form of IMSI modulo1024, and an optional UE specific DRX cycle length. Alternatively, it is also possible to configure a UE specific paging cycle. The connected mode DRX cycle and other DRX parameters (when used) may be configured in the UE through optional parameters typically in the RRCConnectionReconfiguration message, or later in connected mode. A more detailed description of DRX mechanisms can be found in literature, such as in the reference book 4G LTE/LTE-Advanced for Mobile Broadband by Erik Dahlman, Stefan Parkvall and Johan Sköld, Academic Press, 2011, ISBN:978-0-12-385489-6, see e.g. chapter 13.2.6 “Discontinuous Reception (DRX) and Component Carrier Deactivation”. More detailed descriptions of DRX cycles can also be found in, e.g. 3GPP TS 36.304 V.11.3.0 (see e.g. chapter 7), 3GPP TS 36.300 V.11.5.0 (see e.g. chapter 12), 3GPP TS 36.321 V.11.2.0 (see e.g. chapter 5.7). As will be appreciated, the DRX mechanisms are defined for both idle mode and connected mode. Generally speaking, these DRX mechanisms are excellent UE energy saving mechanisms.
However, the inventors have realized that when the communication events are short and infrequent, each communication event is likely to be preceded by an idle to connected mode transition, and this transition is likely to take a significant portion of time from the whole time needed to perform the data transmission. The potential use of long connected mode DRX cycles may increase the risk of radio link failure during mobility between radio cells, which means that idle to connected mode transition may be triggered many times in such scenarios too. In addition, since the connection setup procedure often involves exchange of a large number of signaling messages, this control plane communication is likely to dominate i.e. comprise more messages, larger data volumes and consume more energy, over the user plane communication. Furthermore, since the signaling procedure involves many nodes in the network as well as significant processing in the network nodes, e.g. in order to set the appropriate configuration parameters, the time intervals separating the messages may be significant. Hence, having the MTC device (or other UE) actively listening for downlink transmissions during the entire idle to connected mode transition, due to the lack of DRX sleep mode possibilities, may cause an a relatively high UE energy consumption in many scenarios. In turn, this may have a significant negative impact on the battery lifetime of a UE, e.g. a MTC device.